The present invention relates to preformed stabilizers useful for the production of polymer polyols, to polymer polyols produced from these preformed stabilizers and to processes for the production of these preformed stabilizers and polymer polyols. This invention also relates to a process for the production of polyurethane foams from the polymer polyols produced from the preformed stabilizers of the present invention and to the resultant foams.
Polymer polyol compositions suitable for use in producing polyurethane foams, elastomers and the like are known to those skilled in the art. Such polymer polyol compositions are used to produce two major types of polyurethane foams—slabstock and molded. Slabstock foams are used in the carpet, furniture and bedding industries. Primary uses of slabstock foam are as carpet underlay and furniture padding. High resiliency (HR) molded foam is the type of molded foam generally made. HR molded foams are used in the automotive industry for a number of applications ranging from molded seats to energy-absorbing padding.
Some of the earliest polymer polyol compositions are disclosed in U.S. Pat. Re. 28,715 (reissue of U.S. Pat. No. 3,383,351) and U.S. Pat. Re. 29,118 (reissue of U.S. Pat. No. 3,304,273). These disclosures teach that a stable dispersion of polymer particles in a polyol can be produced by polymerizing one or more ethylenically unsaturated monomer dissolved or dispersed in a polyol in the presence of a free radical catalyst.
The first commercial polymer polyol compositions were produced using acrylonitrile. Many of these acrylonitrile-based compositions possessed such high viscosities that they were undesirable for certain applications. More recently, acrylonitrile-styrene monomer mixtures have been used commercially to make the polymer component of polymer polyols. The expanding demand for polymer polyols has highlighted several product needs and this has spawned additional advances in technology.
Polymer polyols derived from such high styrene monomer mixtures appear incapable of satisfying ever-increasing market requirements for stability and increased load-bearing characteristics in foams. Polymer polyols with increased load-bearing characteristics can be obtained by increasing their polymer or solid contents. Solid contents of from 30 to 60 weight percent, or higher, are desirable. However, polymer polyols having increased solid contents without reduced stability of the polymer polyol and undesirably increased viscosity have not been disclosed in the prior art.
Use of high styrene monomer mixtures and high solid content polymer polyols has generally resulted in polymer polyols having undesirably high viscosity. The viscosity of a polymer polyol should be sufficiently low for ease of handling during its manufacture. In addition, the viscosity should facilitate transport, handling and, ultimately, adequate processability, in the foam processing equipment being used. Increased use of sophisticated mixing systems, such as impingement systems, makes excessive viscosity of the polymer polyol a significant problem. There is therefore a need for lower viscosity polymer polyols which satisfy the increased demands in the art.
As previously indicated, polymer polyol stability is a concern to makers of polyurethanes. At one time, seediness or filterability, a measure of stability of polymer polyols, was not a major issue in commercial practices. However, advances in the state of the art of polyurethane production have resulted in changes to polymer polyol stability criteria, especially in the molded foam area.
With commercial developments in sophisticated, high-speed and large-volume equipment and systems for handling, mixing and reacting polyurethane-forming ingredients, the need for highly stable and low viscosity polymer polyols has evolved. Polymer polyols must meet certain minimum requirements for satisfactory processing in such sophisticated foam equipment. Typically, the prime requirement is that the polymer polyols possess sufficiently small particles that filters, pumps and the like do not become plugged or fouled within relatively short periods of time.
Though there have been advances in reduction in viscosity and increase in solids of polymer polyols, there remains a need for improvement in viscosity reduction and increase in solids content. Greater reductions in viscosity are needed to meet market demands and greater effective increases in solids content are also needed by the market. More importantly, there is a need for technology in polymer polyols that maximizes viscosity reduction while also providing a viable mechanism to higher solids content.
The general concept of using stabilizer precursors in polymerization is disclosed in, for example, U.S. Pat. Nos. 4,454,255 and 4,458,038. The macromer in these patents may be obtained by reacting a polyol with a compound having reactive ethylenic unsaturation such as, for example, maleic anhydride or fumaric acid. Another description of this technique can be found in U.S. Pat. No. 4,460,715. The reactive unsaturation in the stabilizer described in U.S. Pat. No. 4,460,715 is provided by an acrylate or methacrylate moiety.
U.S. Pat. No. 4,242,249 discloses improved polymer polyols prepared by utilizing certain preformed dispersants or preformed stabilizers. These polymer polyols provide stability satisfactory for commercial production, and use of at least one of the following: (1) higher amounts of styrene or other co-monomer when acrylonitrile copolymer polymer polyols are being prepared, (2) higher polymer contents or (3) lower molecular weight polyols.
Other disclosures which describe stabilizer precursors (or macromers) for polymer polyols include, for example, U.S. Pat. Nos. 4,550,194, 4,652,589, and 4,997,857. The stabilizer precursors of U.S. Pat. No. 4,997,857 are characterized by these four features: (1) they are prepared from a starting polyol having a functionality greater than 4; (2) they have at least 60% retained unsaturation; (3) they have viscosities greater than 2000 centipoise at 25° C.; and (4) the starting polyol is capped with ethylene oxide and/or the adduct formed between the starting polyol and a reactive unsaturated compound is capped with ethylene oxide.
A pre-formed stabilizer (PFS) is particularly useful for preparing a polymer polyol having a lower viscosity at a high solids content. In the pre-formed stabilizer processes, a macromer is reacted with monomers to form a co-polymer of macromer and monomers. These co-polymers composed of a macromer and monomers are commonly referred to as pre-formed stabilizers (PFS). Reaction conditions may be controlled so that a portion of the co-polymer precipitates from solution to form a solid. In many applications, a dispersion having a low solids content (e.g., 3 to 15% by weight) is obtained.
Preferably, the reaction conditions are controlled so that the particle size is small, thereby enabling the particles to function as “seeds” in the polymer polyol reaction.
For example, U.S. Pat. No. 5,196,476 discloses a pre-formed stabilizer composition prepared by polymerizing a macromer and one or more ethylenically unsaturated monomers in the presence of a free-radical polymerization initiator and a liquid diluent in which the pre-formed stabilizer is essentially insoluble.
EP 0,786,480 discloses a process for the preparation of a pre-formed stabilizer by polymerizing, in the presence of a free-radical initiator, from 5 to 40% by weight of one or more ethylenically unsaturated monomers in the presence of a liquid polyol comprising at least 30% by weight (based on the total weight of the polyol) of a coupled polyol which may contain induced unsaturation. These pre-formed stabilizers can be used to prepare polymer polyols which are stable and have a narrow particle size distribution. The coupled polyol is necessary to achieve a small particle size (preferably ranging from 0.1 to 0.7 micron) in the pre-formed stabilizer.
U.S. Pat. Nos. 6,013,731 and 5,990,185 also disclose pre-formed stabilizer compositions composed of the reaction product of a polyol, a macromer, at least one ethylenically unsaturated monomer, and a free radical polymerization initiator.